The invention pertains to a generating unit comprising a combustion engine and a generator, the combustion engine having a crankshaft journalled in a crankcase and the generator comprising a generator casing joined to the crankcase, a stator and a rotor coupled to the crankshaft. The generator unit can be a stationary standby unit or a drive unit for a vehicle with electric motors, in particular wheel-mounted motors, supplied by the generator.
In such units, the whole power of the combustion engine is converted into electric power. Accordingly, the dimensions of the generator and the mass of its rotor are substantial. The first increases the weight and bulk of the whole unit, the second makes the unit prone to dynamic interaction between the rotor and the crankshaft. Such units usually employ combustion engines of high power and high specific power. Therefore and in order to allow for the small magnetic gap required for high efficiency of the generator additional support is required.
A generic generating unit is known from the Patent DE 44 04 791 C1. The generator of that unit comprises a cup-shaped rotor and stator windings located inside. The rotor has a central hub, which hub is not rigidly joined to the crank-shaft, but journalled in the generator casing on the far side of the combustion engine and centered with regard to the crankshaft by means of a pin. For the driving connection between the rotor and the crankshaft, a disk is provided, the disk being stiff in a circumferential direction and flexible for longitudinal and angular displacements. The capability of the disk to decouple vibrations is very limited, and further reduced by the centering pin. This pin, however, seems necessary because of the length of the tolerance chain from the crankshaft to the bearing on the far side of the crankshaft through both casings. The pin is a critical element because its strength and precision determine the width of the magnetic gap.
The publication WO 2006/121045 A1 discloses a unit, wherein only part of the engine power is branched of to the generator. Between the end of the crankshaft and an exit shaft, there is a stub shaft carrying the rotor of the generator. The rotational coupling is established by splines and the rotor is journalled in the generator casing on the far side from the combustion engine. This design is marred by the above mentioned tolerance—problem. Over and above it is not suitable for a unit without the journalled exit shaft.
It is the object of the invention to provide a generating unit that, with a minimum of bulk, allows a precise guidance of a rotor dimensioned for the entire power of the combustion engine and does not add any load to the crankshaft. On top of that, the generator must be easy to join to a combustion engine as is used for conventional mechanical drive trains.